

    \filetitle{difflog}{First log-difference pseudofunction}{modellang/difflog}

	\paragraph{Syntax}\label{syntax}

\begin{verbatim}
difflog(Expr)
difflog(Expr,K)
\end{verbatim}

\paragraph{Description}\label{description}

If the input argument \texttt{K} is not specified, this pseudofunction
expands to

\begin{verbatim}
(log(Expr)-log(Expr{-1}))
\end{verbatim}

If the input argument \texttt{K} is specified, it expands to

\begin{verbatim}
(log(Expr)-log(Expr{K}))
\end{verbatim}

The two derived expressions, \texttt{Expr\{-1\}} and \texttt{Expr\{K\}},
are based on \texttt{Expr}, and have all its time subscripts shifted by
--1 or by \texttt{K} periods, respectively.

\paragraph{Example}\label{example}

The following two lines of code

\begin{verbatim}
difflog(Z)
difflog(X{1}/Y{-1},-2)
\end{verbatim}

will expand to

\begin{verbatim}
(log(Z)-log(Z{-1}))
(log(X{1}/Y{-1})-log(X{-1}/Y{-3}))
\end{verbatim}


